Oannes

The Chaldean sea-god. It had a fish's head and body, and also
a human head; a fish's tail, and also feet under the tail and fish's
head. In the day-time he lived with men to instruct them in the arts
and sciences, but at night retired to the ocean. Anedotes or Idotion
was a similar deity, so was the Dagon [dag-On, fish On] of the
Philistines.